3 o 4 THE TANGANYIKA PROBLEM. 



cavity of the first ectodermal invagination of the bud, and 

 quite visible from without. This is the rudiment of the 

 manubrium of the bud. See Fig. 3. About this time the 

 velum becomes perforated in its centre, the four primary 

 tentacles stand stiffly out, and each small medusa, although 

 still not fully formed and attached to the parental manu- 

 brium, pulsates with great vigour. By this time the bud 

 has become much constricted off at its base, and as this 

 tendency becomes greater the endodermal cavity of the 

 manubrial boss breaks through into the cavity of the bell, 

 forming the new manubrium, the gastric cavity of the 

 parent opening for a short space of time actually on to the 

 exterior, through the velum of the bud (Fig. 3). Finally 

 the bud becomes completely detached, and at the point of 

 separation there arises a rapid thickening of the mesoglia 

 which forms the rudiment of the lens characteristic of the 

 adult. This rapid thickening gradually pushes the endoderm 

 lining the bud's gastric cavity up into the gastric cavity, 

 which becomes continually wider and more and more filled 

 up with the growing lens, until the endoderm lining the 

 Moor of the stomach is actually pierced, a small circular 

 portion of the lens protruding through the endodermal 

 lining into the gastric cavity itself as in Figs. 3 and 5. This 

 protrusion rapidly increases, so that eventually the endo- 

 derm merely lines the walls of the shallow and widely-open 

 manubrial tube and a circular ditch round the bulging lens. 

 In buds which have been produced asexually in this manner 

 it is found that, even before the above stage has been 

 reached, their manubriums are already studded with a new 

 generation of buds, which in turn go through the same 

 process. 



There is, however, sometimes to be observed, especially 

 in the solitary parental forms, an interesting modification of 



